EA035228B1 - Method for adaptive data transmission in an industrial controller - Google Patents

Abstract

The invention relates to a method for transmitting information over wire lines in an industrial controller. The method of data exchange consists in exchanging data between the master electronic device (Master) and the slave electronic device (Slave) via a wire channel in the form of control and informational packets that have the attribute of adaptive reading (ADP) entered in their control fields. When transmitting data from the Slave to the Master, the Master device requests the Slave for the number of words of useful information which is equal to the maximum possible number of words needed to record the parameter monitored. In this case, the slave device sends such a number of words of useful information in answer to the request of the master device that is sufficient to record the current value of the monitored parameter. In case the slave device sends less words of useful information than the number of words requested by the master to the master device, the ADP has different meanings in the control and informational packets. The proposed method enables one to transfer fewer words of useful information, which provides a higher rate of data transmission.

Description

The invention relates to a method for transmitting information over wire lines in an industrial controller with programmable logic (PLC), which is a computing and control unit in distributed automated process control systems (ACS).

PLC is designed to collect and process information received from instrumentation in the form of discrete, analog and digital signals, including receiving information from other subsystems of automatic control, and to generate effects on actuators. One of the problems of PLC developers is the provision of highly reliable and high-speed information communication between the central processor module and input-output modules, intended for inputting signals from sensors to the controller and for outputting control signals to actuators. The solution of this problem is devoted to the present invention.

When describing the proposed method and analogues used terms having the following meaning.

Data transfer protocol - a set of rules and conventions that define the content, format, time parameters, sequence and error checking in messages exchanged between system devices.

Master device - a master device that sends data to other users and / or requests data from other users, i.e. is the initiator in the exchange of data with the slave device (Slave).

Slave device - a device that can exchange information only with the master device (Master) after the corresponding request is received from the master device.

Data transmission channel - a set of technical devices (cables, couplers, connectors, printed circuit boards, etc.) that ensure the transmission of messages of any type from the sender to the receiver using electrical signals.

Subscriber - an electronic device connected to a data transmission channel for issuing or receiving data.

A word is a string of bits, considered as a whole when they are transmitted, received, switched, processed, displayed and stored.

A packet is a block of data sent over a data channel.

A control package is a data block processed by network programs as a whole. The package consists of data that plays the role of service information necessary for the implementation of the protocol.

An information package is a data block processed by network programs as a whole. The package consists of overhead information and useful information that must be transmitted.

The general structure of the control or information package is determined by the composition of the package and its format.

Composition - the various data types contained in the package.

Format - dimension and placement order of various data types.

A known method for adapting the reliability of data transmission in a serial bus system (RF patent No. 2597501 C2), adopted as an analogue. Subscribers exchange messages on the bus that have a logical structure that complies with ISO 11898-1 for the CAN protocol. According to this protocol, the message structure includes a frame start bit, an arbitration field, a control field, a data field, a cyclic checksum (CRC) field, a confirmation field, and a frame end sequence. With a free bus, any subscriber can transfer data at any time. In case of simultaneous data transmission by two or more subscribers, access to the bus is arbitrated and a message with a higher priority is transmitted. In connection with the increasing requirements for the transmitted data volumes in a known method, the format of the data field is modified. The format of the data field has been increased from the maximum standard 8 bytes to 16 bytes or up to 24 bytes in the extended format. Due to the possibility of increasing the data field in the transmitted message, the effect is achieved that, in comparison with the corresponding CAN standard message, a larger amount, or volume, of data can be transmitted via the bus. This advantageously increases the ratio of the volume of information (useful information) contained in the message to the volume of service information and thereby also increases the average data transfer rate over the bus system. In the known method, two types of messages are used, the first type using CAN protocol, the second type with a modified data field format. The type of message is determined by the communication controller due to the reserved bit or additional bit or bit combination entered in the arbitration field and / or in the control field. Thanks to this bit, the communication controller adapts its work to receive the appropriate type of message.

Since the claimed method of data exchange (protocol) was originally developed for a controller whose operation is characterized by cyclicity, mandatory polling in the cycle of all I / O modules and guaranteed response time (real-time system), a protocol based on the leading architecture was taken as the basis master (slave), which, unlike the CAN protocol based on the bus arbitration, provides the listed requirements.

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The basis for the proposed method of data exchange is the interface described in the MILSTD-1553B standard, dated 21 September 1978, Department of defense interface standart for digital time division command / response multiplex data bus (designation of the US military standard). In our country, it was approved as GOST 26765.52-87 (replaced by GOST R 52070-2003, entered into force on June 5, 2003). Serial trunk interface of the electronic module system. General requirements (prototype). This standard describes a serial main interface with centralized control used in the electronic module system and establishes requirements for the organization of information exchange, the functions of interface devices and the control of information transfer, the characteristics of the information highway and the characteristics of interface devices. The interface operates asynchronously in command-response mode. Initiation of information exchange and transmission control is carried out only by the bus controller. The standard defines the composition of words (Fig. 1) - the command word, data word and response word. The size of each word is 20 digits. Words begin with a clock signal (three bits), then a data field (16 bits) and end with a parity bit. Two types of sync signals are defined, which make it possible to distinguish command words from information words. All information on the highway is transmitted in Manchester-2 code.

The interface described by GOST R 52070-2003 has the following disadvantages. So, a low information transfer rate of -1 Mbit / s is defined. The maximum size of a message that can be transmitted or received is not more than 32 data words. At the same time, complete control of the reliability of the transmitted information is not provided. Addressed subscribers no more than 31. All this limits the use of the interface according to GOST R 52070-2003 in modern systems.

The objective of the invention is to increase the speed of data transfer and, consequently, the speed of data exchange between electronic devices that implement the claimed protocol.

The technical result is achieved by the fact that between at least one master electronic device and at least one slave electronic device via a data channel, serial data exchange is carried out for the master to read the values of the controlled parameter from the slave device. To do this, first, the value of the monitored parameter is requested from the master device from the slave device, for which a control packet is transferred from the master device to the slave device, which consists of words acting as service information. Then, the value of the monitored parameter is transmitted from the slave device to the master device, for which a data packet is transmitted from the slave device to the master device, which consists of words of service information and words of useful information intended to record the current value of the parameter being monitored. In this case, the service information of the control and information packets contains an encoded number of words of useful information and a bit that is designed to notify the host device of a decrease in the number of words of useful information received by the master in the information packet compared with the number of words of useful information requested by the master in control package. At the same time, when a control packet is transmitted from the master to the slave, it contains the encoded number of the maximum number of words of useful information specified for recording the value of the monitored parameter, and when the information packet is transmitted from the slave to the master, it contains encoded number of words of useful information, which is transmitted to the host device and which is sufficient to record the current value of the monitored parameter. In the event that there is a decrease in the number of words of useful information in the information packet compared with the requested number of words of useful information in the control packet, a bit that is designed to notify the host device of a decrease in the number of words of useful information received by the master in the information packet compared to the number words of useful information requested by the master in the control packet will have different meanings in the control and information packets.

Signs and advantages of a data exchange method are disclosed in the following description of an embodiment of the invention, given with reference to the following drawings, in which:

FIG. 1 - structure of words according to GOST R 52070-2003 (prototype);

FIG. 2 is a structural diagram of the connection of electronic devices that implement the inventive method of exchanging data;

FIG. 3- transmission of logical zero and one in the code of Manchester-2 (prototype and the claimed method); FIG. 4 - clock signals of the control word and data word (prototype and the claimed method);

FIG. 5 - the physical format of the control word (prototype and the claimed method);

FIG. 6 - the physical format of the data word (prototype and the claimed method);

FIG. 7 - structure of the information package (CTL + DATA);

FIG. 8 is a control packet structure (CTL);

FIG. 9 - data packet structure (DATA);

FIG. 10 is a structure of a data recording message in a Slave;

FIG. 11 - message structure reading data from Slave;

- 2,035,228 of FIG. 12 - a message reading data from a slave device (Slave), in which, when measuring the current value of a parameter from a slave device (Slave), the maximum possible number of data words is required to write a controlled parameter (full read from Slave) to the master device (Master) ;

FIG. 13 - a message reading data from a slave device (Slave), in which from the slave device (Slave) is transmitted to the master device (Master) the number of data words sufficient to write the current value of the monitored parameter (adaptive data reading mode from Slave);

FIG. 14 and 15 - a block diagram of the algorithm of the master (Master) when reading data from the slave (Slave).

To implement the data exchange method, at least one master device (Master) 1 and at least one slave device (Slave) 2 connected to the serial data transmission channel 3 are sufficient (Fig. 2). For example, in a PLC, the central processor module acts as a master device (Master) 1, and as a slave device (Slave) an input module 2 and / or an output module 4 can act, and the controller internal bus is used as a data transfer channel 3. In FIG. 2 also shows the devices of the field (lower) level of the industrial control system, namely, the rotational speed sensor 6 connected to the input module 2 and the motor 7 connected to the output module 4.

The development of integrated circuitry has led to the creation of fundamentally new measuring transducers - intelligent sensors (hereinafter ID), containing a converter and a microprocessor in one housing, which allows you to perform basic operations to convert, amplify and process information in the sensor itself. ID is a combination of hardware and software that provides the display of the properties of the control object in the form of some data structure generated as a result of processing the output signal of the measuring transducer according to a certain algorithm. IDs can not only control the measured values, but also carry out their assessment, correction according to certain criteria, control their own characteristics, work in a dialogue mode with the control system, receive commands, transmit measured values, usually in digital form, as well as alarm messages . The ID can provide adaptation (adaptation) to the range of changes in the values of the measured quantity, to the rate of change of the measured quantity, to the influence of influencing factors, including interference, environmental conditions, etc.

As a slave device (Slave) 5 can be an intelligent sensor and / or intelligent electric drive. So in FIG. 2, as a slave device 5, an ID connected directly to the data transmission channel 3 is shown.

All information on the channel is transmitted as well as in the interface in accordance with GOST R 52070-2003, namely in the Manchester-2 code. This self-synchronizing phase-shifted code has a zero constant component, which is very important in high-speed applications. The coding of 0 and 1 is performed not by the level, but by the signal front in the middle of the clock interval (Fig. 3), which allows for bit-wise synchronization of the transmitter and receiver according to the transmitted information in a wide range of carrier frequency deviations.

Just as in the interface according to GOST R 52070-2003, two types of clock signal are defined (Fig. 4), which allow one to quickly and quickly distinguish the control word from the data word and provide word-by-word synchronization of the transmitter and receiver, i.e. unambiguously determine the beginning of words in stream 0 and 1 in the channel.

In FIG. 5 shows a control word format. The control word begins with a clock signal (3 bits), the polarity of the first half of which is positive, and the second half is negative. This is followed by 16 information bits, and the control word ends with a parity bit (P).

In FIG. 6 shows a data word format. The data word begins with a sync signal (3 bits), the polarity of the first half of which is negative, and the second half is positive. This is followed by a 16-bit data field and the data word ends with a parity bit (P).

To transmit signals over short distances, it is proposed to use a low-voltage differential transmission line along the agreed M-LVDS wire line (TIA / EIA-899 (Electrical Characteristics of Multipoint-Low-Voltage Differential Signaling)). M-LVDS transceivers provide high-speed and reliable signal transmission with low power consumption. When using this transmission method to provide communication between the central processor module and the input-output modules located inside the electrical cabinet with a maximum distance of 10 m from each other, the transmission speed can reach 50 Mbps.

To transmit signals over long distances, an RS485 standard interface (EIA / TIA-485-A) can be used. Subscribers here may be remote smart sensors or expansion controllers.

A packet that includes a data field is called an information packet (CTL + DATA). In FIG. 7 shows the overall structure of the information package. The information package consists of a control field, a checksum field of a control field, a data field and a checksum field of a data field. The control field is the data necessary for the subscriber to determine whether he has fulfilled 3,035,228 functions and indicate his status. The control field contains address information, the action to be performed (data transmission or reception), the number of data words, etc.

A packet that does not have a data field is called a control packet (CTL). The control packets can perform the function of the beginning and end of a communication session, acknowledging the receipt of an information packet, requesting an information packet, etc. In FIG. 8 shows a control packet structure (CTL) consisting of a control field and a control field CRC (1) checksum. A word-by-word data transfer is proposed. The control field consists of the first word cw [0] and the second word cw [1]. To ensure the reliability of data transmission, namely to verify the integrity of the control field data, the CRC (1) checksum is used, which has the form of a third word cw [2].

A data packet (DATA) consists of a data field and a CRC (2) checksum of the data field (FIG. 9). Data field (useful information) - actually the data exchanged between subscribers and for the transfer of which a data packet is used. The last word in the data packet is the CRC (2) checksum of the data field, designed to verify the integrity of the data field.

In the process of the exchange of information on the channel between the transmitting and receiving subscribers, the information and control packets are exchanged according to the established rules, called the exchange protocol.

The composition and description of the types of data used in the proposed method of data exchange

Data type Description Management Pack (CTL) The first sixteen-digit control word cw [0] has the following composition: WR / RD WR Record RD - reading - bit of the operation “write” data to the slave (Slave) or operation “read” data from the slave (Slave). Code: 0-record (WRITE) data, 1-read (READ) data. ADP - a bit of adaptive reading of useful information. It takes up one bit of the word. The purpose of this bit is to notify the master (Master) in the “read” operation about a decrease in the number of words of useful information received by the master (Master) in the information packet, compared with the number of words of useful information requested by the master (Master) in the control packet. The value of this bit changes in the slave when sending fewer data words than the master requested. reserved - reserved bits, the logical value of which the developer can set independently. Size - the number η words of data (useful information). It occupies eight bits of the word, which contains the encoded number of the number of data words (useful information) that must be transmitted to the slave (Slave) or received from the slave (Slave).

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The second sixteen-digit control word cw [l] has the following composition: Spaceaddr - a sign of the number of the internal address space of the requested subscriber for writing / reading information. It takes eight bits of a word. Busaddr - sign of the subscriber address on the bus. It takes up seven bits of a word. BusAddr = 127 - broadcast message "ALL". M / s - bit of the initiator of the current transmission on the bus. Code: 0-Active Master (Master), 1- active slave device (Slave). Sign of the control field checksum in the form of a sixteen-bit word cw [2]: CRC (l) (Cyclic Redundancy Chech) - a sign of the checksum of the first cw [0] and second cw [l] control words. It is used to verify the integrity of the transmission of control words. The calculation uses CRC-16 with the OxAOOl polynomial, the so-called CRC-16 Modbus. Data Packet (DATA) DATA - the data field (useful information) has a variable size. A data field consists of a n-number of sixteen-bit data words (DATA). The number (SIZE) of data words in a packet is indicated in the first control word. The number of words in one package is increased to 256 words. CRC (2) (Cyclic Redundancy Chech) - A sign of the data word checksum. It is used to verify the integrity of the transmission of data words. The calculation uses CRC-16 with the OxAOOl polynomial, the so-called CRC-16 Modbus.

The structure of the control packet and data packet described above allowed increasing the number of subscribers on the bus to 128, and the number of internal address spaces to 256.

The content of the transmitted information can be any, subject to compatibility with word formats and message formats.

Data transfer between the master device (Master) and slave devices (Slave) is divided into three phases: parameterization, configuration and data transfer. In the parameterization and configuration phase, it is checked whether the configuration and parameters of the slave correspond to the settings planned in the master. It checks the type of device, the format and length of the transmitted messages, the number of inputs or outputs. In the data transfer phase, the master (Master) must implement the data transfer to the slave (Slave) and the reception of data from the slave (Slave).

Consider the possible types of messages exchanged between the master and slave devices by sequentially transmitting control and information packets to each other.

The first type of message is designed to transfer data from the master (Master) to the slave (Slave) - write data to the Slave (Fig. 10).

The master device (Master) transmits an information packet (with a sign record (WR) in the control field), and the slave device (Slave) receives the information packet, calculates the checksum CRC (1) of the control field and the checksum CRC (2) of the data field and compares

- 5 035228 their values with those received from the master device (Master). Depending on the result of the checksum comparison, the slave device either ignores the data recording task or accepts it for execution. If the information packet is received correctly, the slave sends a response in the form of a control packet (CTL) to the master. If the checksums do not match, then it is considered that the integrity of the transmitted information is violated and the slave device (Slave) ignores the job and does not send a response.

The second type of message is designed to transfer data from the slave device (Slave) to the master device (Master) - reading data from the Slave (Fig. 11).

The master device (Master) transmits a control packet (with a read sign (RD) in the control field) and releases the channel. The addressed slave device (Slave) receives the control packet, calculates the CRC (1) checksum of the control field and compares its value with the value of the checksum received from the master (Master). Depending on the result of the checksum comparison, the slave device either ignores the data transfer job or accepts it for execution. Upon successful comparison, the slave device (Slave) captures the bus and transmits to the master device (Master) a response in the form of an information packet. The master device (Master) receives a response from the slave device (Slave) in the form of an information packet and calculates the checksum CRC (1) of the control field and the checksum CRC (2) of the data field. Upon successful comparison of the checksums, the control packet from the slave (Slave) is considered accepted, the data reading by the master (Master) from the slave (Slave) is completed.

It is known that for a data exchange method in which one subscriber (Master) always proactively requests data from another subscriber (Slave), it is characteristic that the subscriber (Slave) always sends the subscriber (Master) as many words of useful information that he has requested from him subscriber (Master) in the current message. In turn, the subscriber (Master) always (from cycle to cycle) asks for the maximum possible number of words of useful information, i.e. requests the number of words of useful information necessary to record such a value of the controlled parameter for which the maximum number of words of useful information is required.

The value of the controlled parameter, measured with a given accuracy, is useful information.

The main idea of the invention is to transmit on the channel only the necessary number of words of useful information, while traditionally in Master / Slave systems the maximum possible number of words of useful information is transmitted.

The proposed method of data exchange makes it possible, when reading data from a slave device (Slave), to transmit over the channel only as many words intended for recording useful information that are sufficient to record the current value of the monitored parameter, which increases the performance of the channel (internal controller bus).

For example, when reading data from a slave device (Slave), the master device (Master) requests the value of the measured (controlled) parameter, for example, the temperature value. Assume that to transmit the temperature limit value, for example T _max = + 70 °, the maximum number of words is required, namely four words (Fig. 12). Therefore, for reading, the control packet (CTL) is sent from the master (Master) to the slave (Slave), where the number five is encoded in SIZE. Those. an information packet is requested from the slave (Slave), the data field of which should consist of four words (d [0], d [1], d [2], d [3]) + one word of the CRC checksum (2) (mode full reading) (Fig. 12). But the range of nominal values of the measured temperature parameter in 90% of cases does not go beyond the values of ° С +21 ... + 40. To record the nominal temperature values, one data word is required. Therefore, each time the nominal temperature value is transmitted, three extra words are sent through the channel, the bits of which are set to logical zero. In order not to transmit unnecessary words in the microprocessor of the slave device (Slave), the current value of the measured temperature is analyzed, for example T ₁ = + 25 °, and the number two is set in the response information packet in SIZE. Those. the slave sends a data packet to the master (Master), in which the data field consists of one data word (d [0]) + one CRC checksum word (2) (adaptive data reading from Slave) (Fig. 13 ) As a result, we have a reduction in the service time & Tr of a specific slave device (I / O module, ID) by about 28%.

The percentage time gain & Tr can be calculated by the formula:

ΔΤρ = (1 - ^) * 100 [%] where x is the maximum number of data words reserved for this monitored parameter;

y is the minimum required number of words for the current value of the controlled parameter.

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In order for the master device (Master) not to perceive the received information packet with fewer words of useful information as an error, the ADP bit is included in the control fields of the control and information packets. The ADP bit is designed to notify the master device (Master) about a decrease in the number of words of useful information received by the master (Master) in the information packet (CTL + DATA), compared with the number of words of useful information requested by the master (Master) in the control packet ( CTL). In the above example, a control packet (CTL) is sent from the master (Master) to the slave (Slave) with a value of 0 in the ADP bit and a specified maximum number in Size of the requested number of words of useful information. In turn, when transmitting from the slave device (Slave) to the master device (Master) the response information packet (CTL + DATA) with the number of words of useful information (DATA) less than that requested in the control packet, the ADP bit in the response information packet has value 1. The received information packet, in the control field of which the ADP bit has the value 1, is considered by the master device as a command to receive another number of words of useful information (Figs. 14, 15). If the slave device sends to the master device (Master) as many words of useful information (DATA) as the master device requested, then the value of the ADP bit in the response information packet does not change and stores the value 0.

Claims (1)

A method of sequential data exchange, which consists in the fact that between the at least one master electronic device and at least one slave electronic device, a data exchange is carried out on the data channel for the master to read the values of the monitored parameter from the slave, for which purpose first from the master they request the value of the controlled parameter from the slave device, and then from the slave device transmit the value of the controlled parameter to the master device, characterized in that for the master to read the values of the controlled parameter from the slave device, the control packet is transmitted from the master device to the slave device, which consists of words performing the role of service information, and then transfer from the slave device to the master information package, which consists of words of service information and words of useful information intended to record the current the values of the controlled parameter, while the service information of the control and information packets contains an encoded number of words of useful information and bits, which is designed to notify the host device about the reduction in the number of words of useful information received by the master in the information packet, compared with the number of words of useful information, requested by the master in the control packet, while when the control packet is transmitted from the master to the slave, it contains the encoded number of the maximum number of words of useful information specified for recording the value of the parameter being monitored, and when they are transferred from the slave to the master information package, it contains such an encoded number of words of useful information that is transmitted to the host device and which is sufficient to record the current value of the monitored parameter, and in the case if there has been a decrease in the number of words of useful information in the information packet compared to the requested number of words of useful information in the control packet, a bit that is intended to notify the host device of a decrease in the number of words of useful information received by the master in the information packet compared to the number of words of useful The information requested by the master in the control packet will have different meanings in the control and information packets.